Field of the Invention
The present invention relates to fingerprint recognition apparatus, especially to a fingerprint recognition apparatus with high sensitivity.
Description of Related Art
Biometric recognition technologies have rapid development due to the strong request from electronic security applications and automatic access control system. The biometric recognition technologies can be classified into fingerprint recognition, iris recognition, DNA recognition, and so on. For the considerations of efficiency, safety and non-invasiveness, the fingerprint recognition becomes main stream technology. The fingerprint recognition device can scan fingerprint image by optical scanning, thermal imaging or capacitive imaging. For cost, power-saving, reliability and security concerns, the capacitive fingerprint sensor becomes popular for biometric recognition technology applied to portable electronic devices.
The conventional capacitive fingerprint sensors can be classified into swipe type and area type (pressing type), and the area type has better identification correctness, efficiency and convenience. However, the area type capacitive fingerprint sensor generally integrates the sensing electrodes and the sensing circuit into one integrated circuit (IC). FIG. 1A shows a sectional view of a related art capacitive fingerprint sensor, which comprises a package substrate 102A, a fingerprint recognition IC 100A and a sapphire protection film 140A. The fingerprint recognition IC 100A is arranged on the package substrate 102A and has a sensing area with a plurality of sensing electrodes 110A. The sensing electrodes 110A are arranged on a surface of the fingerprint recognition IC 100A, which is closer to the user finger. The conductive pads 120A of the fingerprint recognition IC 100A are electrically connected to the corresponding conductive pads 104A on the package substrate 102A through the lead-out wires 130A. To protect the lead-out wires 130A, a sealing resin 150A is used to encapsulate the lead-out wires 130A. However, the distance between the finger and the sensing electrodes 110A will be increased by the height h1 (in the order of tens of micro meters), and this has great impact on the sensing accuracy. The area along the height h1 needs to be filled with expensive sapphire protection film 140A with high dielectric constant. This will increase cost and the extra distance h1 renders the capacitive fingerprint sensors difficult to be integrated below the protection glass.
FIG. 1B is a sectional view of another related art capacitive fingerprint sensor, where the capacitive fingerprint sensor is packaged into an electronic device with a protection glass 20A having thickness h2. Due to the protection glass 20A, the distance between the finger and the sensing electrodes 110A will be increased by the height (h1+h2). A common solution to reduce the distance is to dig hole in the protection glass 20A and then embed the fingerprint recognition IC 100A into the hole. However, material cost and fabrication complexity are increased while the yield, lifetime and durability of the product are reduced. It is development trend to enhance sensing accuracy and signal-to-noise ratio to advantageously increase the distance between the finger and the sensing electrodes. Moreover, it is desirable to place the fingerprint recognition IC below the protection glass to reduce cost and enhance the lifetime and durability of the products.
It is an object of the present invention to provide a fingerprint recognition apparatus with low cost and high performance. The sensed signals are led out through metal bumps to reduce the sensing distance by tens of micro meter, which is caused by the conventional lead-out wire. The packaging complexity and cost are reduced while the sensing accuracy is enhanced. Another object of the present invention is to provide a fingerprint recognition apparatus with flexible and simple process.